Basics of Vitrification: Egg and Embryo Freezing


Egg and Embryo Freezing at CNY Fertility - State of the Art Fertility LabBasics of Vitrification:
Advances in biotechnology over the past decade have made it possible to preserve human embryos and unfertilized human oocytes (eggs) through a process called vitrification. Vitrification technology freezes cells at an ultra-rapid rate.
Over the last five years, there has been an outstanding shift in fertility preservation practices worldwide from slow freezing embryos to fast freezing them through vitrification. CNY Fertility, with offices in Syracuse, Albany and Rochester, NY, has been utilizing vitrification as the sole method to freeze embryos since 2009.
Slow freezing has successfully preserved human embryos for nearly 30 years, beginning in Australia in 1984, by cooling them at a rate of just 0.3C per minute until their temperature drops below -30C. But first, cryobiologists had to avoid the formation of ice crystals in the fluids in the cells as the water in them turned to ice. These razor-sharp ice crystals are deadly to cells for two reasons: they can kill cells by shredding any cell membranes and by rupturing them as water turns to ice in the cells, expanding their volume.
To solve this problem, slow freezing methods incubate embryos in chemicals called cryoprotectants. Prior to freezing, cryoprotectants – such as ethylene glycol and glycerol — draw water out of a cell by simple osmosis and then replace the water in the cell. This swapping act avoids or limits much of the formation of ice crystals in a cell.
Embryo Vitrification:
Before freezing, vitrified embryos are exposed to 5-10 times more cryoprotectant than embryos that are slow frozen.  Cryoprotectants cause hardening of the shell surrounding an embryo or egg. Once thawed and placed in the uterus, an embryo will have to escape from the shell. Assisted hatching is a procedure in which a fine laser is used to make a hole in the shell prior to transferring the embryo. This procedure helps avoid complications associated with hardening of the shell. Since the shell is a non-living part of the embryo, assisted hatching does not damage the embryo.
Oocyte Vitrification:
Oocytes (unfertilized eggs) are exposed to high concentrations of cryoprotectant in a slower, step-wise approach, designed so the oocytes can survive freezing as well as human embryos can. The eggs are bathed in a series of cryoprotectant solutions with increasing concentrations, and when the eggs are placed in the last cryoprotectant solution, they are instantaneously frozen. Once thawed, the eggs must be fertilized using ICSI.
While embryo freezing is still the preferred technique for fertility preservation, young or single women with cancer who don’t want to use a sperm donor at that time may want to freeze their eggs instead. Young women may also choose to preserve their healthy eggs in preparation for motherhood at a later time when age-related fertility issues may affect them.
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